1. Field of the Invention
The invention relates to an adhesive composition for bonding an optical fiber to a suitable housing using light, in the visible and near-infrared ranges of the spectrum, to cure the adhesive. A colorant included in the adhesive composition provides evidence that the space between the optical fiber and the housing is filled prior to curing. The colorant further signals the point at which exposure to a light source is sufficient to cure the adhesive and bond the optical fiber within the housing.
2. Description of the Prior Art
Successful use of optical fiber cables for carrying, e.g. telecommunication signals depends upon maintaining axial alignment of the fiber along the length of the cable even though it may be subject to junctions held together by suitable connector or termination structures. Correct positioning of the optical fiber, within the connector or termination structure, represents a critical requirement for maintaining maximum signal transmission across a junction of precisely aligned fibers. Precise alignment relies upon the retention of a fixed spatial relationship between the fiber and the connector structure. When accurately established, correct spatial relationship ensures desirable fiber-to-fiber alignment during junction formation using interlocking connector or termination structures which may be subject to repeated engagement and disengagement. A convenient means to establish the correct spatial relationship between an optical fiber and a connector involves the use of a bonding material, usually an adhesive, for securing the fiber to an inner surface of the connector structure.
There are many examples of the use of adhesives, of various kinds, for bonding optical fibers inside connector structures. U.S. Pat. No. 4,588,256 discloses the use of hot melt adhesive, contained in an optical fiber mounting means, inside a connector. Upon heating of the optical fiber mounting means, the hot melt adhesive softens, allowing insertion of the optical fiber which becomes bonded to the mounting means when the adhesive cools and solidifies. Similarly, U.S. Pat. Nos. 4,984,865 and 5,048,915 employ thermoplastic adhesives for bonding an optical fiber within a connector structure. In both cases, a small amount of molten adhesive exudes from the tip of the connector under the force of insertion of the optical fiber into the heated thermoplastic adhesive. Upon cooling, a small drop of adhesive surrounds the glass fiber, at the tip of the connector. This drop formation, while suggesting that adhesive surrounds the optical fiber, does not provide confirmation that adhesive fills the connector. Such filling of the connector, to place adhesive in the space between the optical fiber and the inner wall of the connector, provides the optimum condition for securely bonding the fiber to the connector. Less than optimum bonding could lead to disruption in the position of the fiber relative to the connector with resultant loss of alignment between fibers present in connectors used to join lengths of optical cable together.
A means to indicate optimum bonding between optical fibers and connecting structures would be advantageous towards providing reliable optical fiber connections. Suitable indicating means would confirm bond formation capable of surviving forces associated with shock or extension of a connection. The current invention provides a means of indicating optimum bond formation using an colored adhesive composition, which, during bonding of the optical fiber inside a fiber connector structure, shows uniform coloring when the adhesive fills the space between the fiber and the connector in a first color. The adhesive is subject to curing by exposure to visible light, and as it cures, the first color changes to a second color at the initiation of cure.
Further, such adhesive should be of a viscosity small enough such that it is injectable, however, large enough, such that when injected it will remain in the desired area of the connector and not migrate to other areas.